The Chelsea coach admitted his disappointment at not taking three points from the Old Lady having been 2-0 up but hailed the Brazilian playmaker who scored twice on his full debut
The 21-year-old netted a deflected strike on the half-hour mark, and followed it up minutes later with a superb effort to fully announce himself at Stamford Bridge.
While Di Matteo was delighted with his starlet's performance, the former midfielder was frustrated at throwing away a two-goal lead to end matchday one with a point, rather than three.
"[It was] a terrific debut for him," Di Matteo told Sky Sports. "We were just waiting for the right game for him to be put into the team, and it was wonderful to watch him tactically as well.
"He played a very big role for us today and scored, and the second one was fantastic as well.
"I thought it was a very good football game and at the end, probably both teams could have won it. We had chances to go with the third goal and probably close the game, and then they equalised, but I think it was probably a deserved draw.
"We probably made a couple of mistakes on their goals and then the good movement and quality finish as well.
"It's a disappointment. We found ourselves in a great position to win the game and we only got a draw. But we knew we were playing against a quality side and they have a lot of good players.
"We feel a little bit deflated at the moment because obviously we were ahead and you come off with a draw, but it's going to be a tough group, we know that, and we get on to the next game now."